The invention relates to the field of focusing mechanisms, and more particularly to a focusing mechanism for an ophthalmoscope or other suitable optical instrument.
As is well known, ophthalmoscopes are medical diagnostic instruments which are used for examining the eyes. An indirect small pupil ophthalmoscope, for example, as described in U.S. Pat. No. 6,065,837, includes an instrument housing which retains a light source as well as a set of lens modules and an eyepiece. The eyepiece should be adjustably movable in order to adjust the position of the eyepiece focal plane relative to the image of the retina of a patient""s eye being viewed to compensate for the refractive error of either the patient or the physician.
Several prior art mechanisms are known for axially adjusting the position of an eyepiece. Each, however, is relatively complex in design requiring many different components or extreme dimensional tolerancing in order to function adequately. Simpler designs requiring a manual focus adjustment member do not appear to relieve any backlash, which makes axial adjustment difficult or produces lateral or other loads on the eyepiece or the mechanism that cause axial adjustment to be imprecise.
It is a primary object of the present invention to improve the field of optical instruments.
It is a further primary object of the present invention to improve the operation of the focusing mechanism of an optical instrument such as an ophthalmoscope.
It is yet a further primary object of the present invention to produce a manual focusing mechanism for an optical instrument which provides the correct ratio of thumbwheel motion to eyepiece motion while minimizing backlash in the focusing mechanism as well as lateral loads induced on the eyepiece.
Therefore and according to a preferred aspect of the present invention, there is described a focusing mechanism comprising:
a eyepiece having at least one lens element retained within an eyepiece housing;
a stationary carrier for retaining said eyepiece;
a movable thumb wheel operatively connected to said stationary carrier; and
at least one lever operatively connecting said eyepiece housing and said thumb wheel, said thumb wheel including a cam channel for receiving a first end of said at least one lever, and in which an opposing second end of said at least one lever engages said eyepiece housing, such that rotational movement of said thumb wheel produces corresponding axial movement of the eyepiece relative to the stationary carrier.
Preferably, a pair of levers interconnect the thumb wheel with the eyepiece, the levers each having first ends which engage a corresponding spiral cam channel that is provided on each side of the thumb wheel. The eyepiece includes a channel which receives an opposing second end of each corresponding lever. As the thumb wheel rotates, the engagement members of each of the levers track within the spiral cam channels. Based upon a hinged mount of the levers to the stationary carrier, the levers are caused to pivot, thereby producing effectively axial motion of the remaining ends of the lever and controlled axial motion of the eyepiece. According to this embodiment, the pivoting axis of the levers and the mounting axis of the thumb wheel are each substantially perpendicular to the optical axis of the instrument, but do not intersect with the optical axis of the instrument. Moreover, second or top ends of the levers are preferably substantially aligned with the centerline (e.g. the optical axis of the instrument) of the eyepiece housing.
More preferably, each of the first ends of the levers include split bosses or fingers which more adequately insure simultaneous engagement with each side of the spiral channel of the thumb wheel. The engagement of the split bosses thereby reduces backlash transmitted to the eyepiece as a result of the rotational motion of the thumb wheel. The split fingers could also be provided at the opposing ends of the levers; that is, the ends in contact with a receiving channel of the eyepiece housing, if desired, to produce a similar benefit.
In the meantime, the eyepiece is retained in radial biasing engagement within the stationary carrier. According to a preferred embodiment, the carrier includes at least one integral spring finger which imparts a radial load on the eyepiece when installed in the carrier. This radial load effectively retains the eyepiece while permitting the eyepiece to track axially along guide surfaces which are provided on the interior of the stationary carrier.
According to another preferred aspect of the present invention, there is described an optical instrument comprising:
an instrument housing;
an eyepiece;
a stationary carrier disposed within said instrument housing and sized for retaining said eyepiece;
a rotatable thumb wheel operatively connected to said stationary carrier; and
at least one lever operatively connecting said eyepiece and said rotatable thumb wheel, said thumb wheel including a cam channel for receiving a first end of said at least one lever, and in which an opposing second end of said at least one lever engages said eyepiece such that rotational movement of said thumb wheel produces corresponding axial movement of the eyepiece relative to the stationary carrier.
Preferably, a pair of levers operatively interconnect the eyepiece and the thumb wheel, the levers being hingably attached to the stationary carrier. First ends of the levers are retained within spiral cam channels of the thumb wheel, with each lever being disposed on an opposite side of the thumb wheel. Second ends of the levers engage the eyepiece. As the thumb wheel rotates, the levers track the spiral cam channels, producing hinged motion of the levers and axial movement of the eyepiece.
Preferably, the first ends of the levers are split, thereby defining split fingers which simultaneously engage the sides of each spiral cam channel. The eyepiece is effectively biased radially within the stationary carrier into guide surfaces defined in the interior of the carrier which facilitates controlled axial movement based on a given rotation of the thumb wheel. More preferably, stops are provided at ends of the spiral cam channel which engage the stationary carrier so as to impart loads onto the levers or the eyepiece at the ends of travel. Alternately or in combination with the above, the second or top ends of the levers can also be spilt to provide simultaneous engagement with the sides of each receiving channel of the eyepiece housing. Still more preferably, the top ends of each of the levers are substantially aligned with the centerline of the eyepiece housing; that is, with the optical axis of the instrument.
According to yet another preferred aspect of the invention, a method of axially adjusting an eyepiece of an optical instrument relative to an optical axis of said instrument is provided. The method includes the steps of:
retaining an eyepiece housing in a stationary carrier, said stationary carrier being operatively connected to a rotatable thumb wheel;
linking a first end of said at least one lever to said rotatable thumb wheel and a second end of said at least one lever to said eyepiece housing, said at least one lever being hingably attached to said stationary carrier; and
rotating said rotatable thumb wheel, causing the first end of said at least one lever to track a spiral channel of said thumb wheel, pivoting said at least one lever about the hingable attachment to said stationary carrier to produce axial movement of said eyepiece.
An advantage of the present invention is that the described focusing mechanism permits thumb wheel rotation in order to effectively move the eyepiece without producing incidental lateral or side loads and with a minimum of backlash.
Another advantage of the present invention is that the above focusing mechanism is relatively simple to manufacture; and does not require excessive dimensional tolerancing; for example, the spiral channel of the rotatable thumb wheel. As a result, the above focusing mechanism is also more inexpensive to manufacture and maintain than other prior known mechanisms.
Yet another advantage provided by the present invention is that the above described mechanism can be utilized in literally any optical instrument requiring an eyepiece.
These and other objects, features, and advantages will be readily apparent from the following Detailed Description which should be read in conjunction with the accompanying drawings.